Annular glass plate, method for manufacturing glass substrate for magnetic disk, glass substrate for magnetic disk, and magnetic disk

An annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm,

• wherein the outer circumferential edge surface and the inner circumferential edge surface each have an arithmetic average surface roughness Ra not larger than 0.1 μm and the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface,
• the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate, and
• the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface by at least 0.01 μm.

An annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm,

• wherein the outer circumferential edge surface has the arithmetic average surface roughness Ra not larger than 0.05 μm, the inner circumferential edge surface has an arithmetic average surface roughness Ra not larger than 0.1 μm, and the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface by at least 0.01 μm,
• the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate, and
• the surface roughness of the inner circumferential edge surface is not less than 0.02 um.